Method of determining oxygen concentration in steel



April 4, 1950 L. FINE 2,502,621

METHOD OF DETERMINING OXYGEN CONCENTRATION IN STEEL Filed Oct. 8, 1945 Patented Apr. 4, 1950 METHOD OF DETERMINING OXYGEN CONCENTRATION IN STEEL Leslie Fine, Burbank, CaliL, minim to Menasco Manufacturing Company, Burbank, corporation of California CaliL, a

Application October 8, 1945. Serial No. 620,944

This invention relates to a process of determining the presence of oxygen in steel and more particularly for determining faulty steel structure due to the presence of oxygen or dissolved oxide concentrations. The particular problem toward which this invention is directed in its specific application is the determination of faulty welds due to the inclusion of oxygen or oxides in or near the weld region. In welding it has been determined, among other things, that what may be referred to as a poor weld has a direct relationship to the amount of oxygen which has been included in the steel, either as free oxygen or as the oxide of the metal prior to or during the formation of the weld.

It is an object of this invention to provide a method of inspection of steel to determine the presence ,of oxygen or oxides dissolved therein, particularly in a Weld area.

Another object of this invention is to provide a method of treatment of a surface which will make visible for inspection the condition of a steel surface so that the oxygen content of such surface will be easily discernible.

Another object of this invention is to provide an eflicient, easily performed, and inexpensive procedure for determining areas of oxygen content in steel.

Another object of this invention is to provide a method of etching a steel surface which is selectively operative to produce a resultant surface upon which the areas of an oxygen content can easily be observed.

. Another object of this invention is to produce a method of determining faulty welds through the treatment of the weld with a selective etching solution which will make easily observable areas of oxygen content included within the weld.

Other objects and advantages of this invention it is believed will be apparent from the following detailed description of the preferred embodiment thereof.

The drawing are reproductions of photomicrographs of welded surfaces or of heated samples of steel treated in accordance with my invention.

In these drawings 7 Figure 1 is a photomicrograph of a cut made through an oxy-acetylene pressure weld of two steel members which has been etched in accord- Claims. (Cl. 41-42) was exposed to the air is of 250.

Figure 3 is a photomicrograph at the magnification of 250 of an oxy-acetylene pressure welded joint formed between two tubular sections of steel, the photograph being of 'a cross-section through inside surface of the weld after treatment of the sample with the alkaline chromate etching solution; Y L

In the preferred embodiment of my invention I determine the presence of oxygen concentrations in the steel by treatment of the steel with a selective agent which is of high alkalinity and which at the same time has the ability to dissolve an appreciable amount of one or more certain anions or which is of suflicient alkalinity as to enance with my invention, the photomicrograph being of magnification.

Figure 2 is a photomicrograph of a piece of steel heated in air to above 2000 F. for over two hours. A cross-section through the surface which as able a selective etching to be formed electrolytically withvor without the addition of such anions to the solution.

I have found that solutions of sodium or potassium hydroxide produce the required alkalinity to produce the selective etching when any one of the following anions are added. The anions which have been found suitable to perform the selective etching in the solution of high alkalinity are:

. Chromate anion Permanganate anion Nitrate anion Peroxide anion Picrate anion Ferricyanide anion As a specific example of the etching solution which I prefer to use, the following is given:

A solution is prepared of sodium hydroxide in water containing 30t0 grams of NaOH per 100- cc. of water and containing chromium trioxide which provides the anion concentration of the solution of from to 50 grams per 100 cc. of water, where the chromate anion is added to the solution as chromium trioxide. The temperature of the solution is preferably maintained between 45 and 158 C. and the steel, the oxygen concentration of which is to be'determined, is immersed in this solution for a period of time of from 15' seconds to one hour. Where the etching is carried out electrolytically, the current density employed is from .1 to 5 amperes per square inch of surface being-treated using a voltage of 1.2 to 4 volts, and the current is passed into the solution while the sample is immersed therein.

The following specific examples are given as illustrative of the results obtained employing the process of my invention.

shown at a magnification In Figure 1 there is illustrated a welded surface which was deliberately produced so as to insure the inclusion of oxygen in the steel forming the weld.- The weld made was an oxy-acetylene weld formed under conditions where pressure was employed to force the two portions of steel together during heating. Sufllcient air was available at the weld surfaces during heating to insure a high oxygen content in the region of the weld.

Figure 1 is a photomicrograph of 100 magnification taken across the weld so formed and where the metal has been treated to selectively etch the same employing my preferred solution made up as follows:

11 grams of chromium trioxide, 53 grams sodium hydroxide,

were added to 100 cc. of water, producing a solution having a boiling point of approximately 117 C. The solution thus prepared may be used at the boiling point or it may be allowed to concentrate to increase the boiling point to 120 C. at which it is preferably kept by the addition of the necessary water.

The time required for the etching of the sample varies from between 2 to 25 minutes, depending upon the size and heat treatment of the steel sample: The particular sample illustrated in Figure 1 was treated in such a solution for a period of twelve minutes.

The areas of the steel surface of the photomicrograph show the selective etching formed by the solution and the white area 1 at the weld shows that a poor weld was performed and that oxygen was included in the two surfaces. The

a white area 1. and the white area 2 at the edge of the materials being welded show the high oxygen inclusion in the metal subjected to the high weld temperature. The base or unaffected metal 3 etches dark. The particular sample illustrated in this photograph was a weld of two tubular sections and the edge 2 is the interior edge of the tubular materials.

It is observed that the selective etching performed by the alkaline chromate solution is selective to portions of the metal leaving the areas in which the oxygen is included as dissolved oxygen or as combined oxygen white so that it can easily be observed.

Figure 2 is a photomicrograph at 250 magnification of a sample of steel which was heated in a furnace to a temperature above 2000 F. and allowed to air cool. A cross-section of the sample was then obtained by cutting perpendicular to the exposed surface, the sample' then being etched in the alkaline chromate solution in the same manner as set forth in the example of the photomicrograph of Figure 1. A chemical determination was then made of the amount of dissolved oxygen or oxides present in the white'areas and this chemical determination was carried out as follows:

The surface was treated by sand-blasting to remove the outer scale and approximately 100 mgs. of the surface steel was dissolved in 6 normal hydrochloric acid.' The amount dissolved was carefully determined by weighing the amount before and after solution. The removal of approximately 100 mgs. of metal did not penetrate the white area and this fact was determined by a microscopic examination of the remainder of the samples. After sampling in this manner, iron determinations were obtained showing that the white area ranged from 87 to 90% in iron content. The steel was determined to have ap- 4 proximately 97% Fe content before the heat treatment. This determination showed that there was included in the metal of the surface 7 to'10% by weight of oxygen present either as free oxygen or as combined oxygen combining with the ferrous metal of the surface.

From the photomicrograph of Figure 2, it will be seen that the outer area 4 illustrates the scale formed upon the surface of the steel sample during the heating thereof. The white area 5 which is beneath the scale 4 shows the depth to which, or at which, oxygen was included in the surface by the heat treating process. This process consisted of heating to above 2000 F. in an electric furnace into which air was freely admitted so that it is definitely established that the excess oxygen present in this atmosphere was included in the surface.

In Figure 3 I have shown a photomicrograph taken at 250 magnification of a cross-section of an oxyacetylene pressure welded Joint between two tubular samples. The white area 6 through the middle of this photograph shows the faultiness of the weld due to the high inclusion of oxygen in the metal forming the joint. The fact of my inclusion of oxygen in the metal of the joint is shown by the white area extending from the two surfaces which were joined together by the welding process. The depth of penetration of oxygen on either side of the weld in this sample is shown by the white veinlets running out from the two sides of the main white area. The sample prior to taking of the photomicrograph was etched with an alkaline chromate etching solution substantially of the same character as utilized in etching the sample illustrated in the photomicrograph of Figure l.

Similar treatments have been made using a solution made up of 40 grams of caustic soda, 3

40 grams of picric acid dissolved in 150 cc. of water in which solution the steel Sample was immersed for a period of 20 minutes, permitting the solution to concentrate while its boiling point increased from 107 C. to 114 C.

The results obtained from this etching of the steel are not as definite as those obtained through the treatment of the alkaline chromate etching solution as hereinabove disclosed but were sum-.

cient to reveal the white zones in the weld produced by the inclusion of oxygen.

The most effective strength of the alkaline chromate solution found was where the solution was made up of approximately 80 grams of caustic soda, 16 grams of chromic acid dissolved in 150 cc. of water, and where the sample is allowed to remain immersed in the solution for a period of 10 minutes while the temperature is maintained between 118 and 120 F. Such treatment gives the most profound definition of the white areas formed by the inclusion of oxygen during the heating or welding of the steel.

A satisfactory alkaline etching solution was prepared using 2 grams of potassium permanganate, 53 grams of sodium hydroxide dissolved in 100 cc. of water, where the sample was immersed in the solution for 7 minutes at a temperature of 119 C. Sodium nitrate, sodium hydroxide solutions also produced useable results in identifying the white areas of inclusion of oxygen in the weld region.

It was generally found using the solutions as hereinabove identified that it was necessary in order to obtain useable results that the alkalinity of the solutions should be in excess of 25 grams of sodium hydroxide per cc. of water and 5 that the temperature of treatment should be above 50 C. up to the boiling point of the particular solution. This is for a chromium trioxide (CrOa) concentration of 11 grams per 100 cc. of water, using a maximum etching time of 1 hour.

The foregoing data are given for the purpose of showing the range of concentrations, times and temperatures which have been found useable in carrying out the process embodying my invention and not as a limitation thereof as for different concentrations of chromium trioxide and different etching times other concentrations may be found satisfactory:

It has been found generally that where it is not desirable to elevate the temperatures of the solutions that satisfactory results maybe obtained through the use of the electrolytic process where -a current is passed through the solution during the time of immersion therein, permitting the etching process to be carried out at nearly room temperature. Under such cases I have found that only a relative current density is required ranging from .1 ampere to 5.0 amperes per square inch in a circuit, the voltage of which may range from 1.2 to 4.0 volts.

Having fully described my invention, it is to be understood that I do not wish to be limited to the details herein set forth, which are given for the purpose of setting forth satisfactory operating conditions of the method embodying my invention, but my invention is of the full scope of the appended claims.

I claim:

1. The method of determining the presence of oxygen in steel, which comprises immersing the steel in a solution of high alkalinity and containing anions selected from the group consisting of chromate, permanganate and nitrate to etch the surface and reveal the oxygen included portions thereof as white areas.

2. In a process of determining the inclusion of oxygen in steel, the steps of subjecting the steel to an etching process in an alkaline solution of a chromate at an elevated temperature for a period of time to produce white areas'in which oxygen is included in the steel.

3. In a process of determining the qualities of a weld, the steps of treating the weld with an alkaline solution containing an alkali hydroxide selected from the group of sodium and potassium hydroxide and which solution includes chromate anions at an elevated temperature and for a period of time sufficient to etch the surface.

4. In a process of determining defective welds due to the inclusion of oxygen therein, the steps of treating the welded surfacein an alkaline solution containing a chromate at an elevated temperature and for a period of time sufllcient to etch the surface, leaving visible white areas of oxygen included in the steel.

5. In a process of determining the presence of included oxygen in steel, the steps of treating the steel in a solution composed of an alkali hydroxide selected from the group consisting of sodium and potassium hydroxide carrying anions selected from the group consisting of chromate, permanganate and nitrate.

LESLIE FINE.

REFERENCES CITED The following references are of record in the file of' this patent:

UNITED STATES PATENTS Kappes Sept. 5, 1939 

1. THE METHOD OF DETERMINING THE PRESENCE OF OXYGEN IN STEEL, WHICH COMPRISES IMMERSING THE STEEL IN A SOLUTION OF HIGH ALKALINITY AND CONTAINING ANIONS SELECTED FROM THE GROUP CONSISTING OF CHROMATE, PERMANGANATE AND NITRATE TO ETCH THE SURFACE AND REVEAL THE OXYGEN INCLUDED PORTIONS THEREOF AS WHITE AREAS. 